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a question on EDR

steamfitter Member Posts: 156
As I understand it 1 EDR is the equivalent of 240 BTU's per square ft. of radiation when there is 215 degrees F of steam and 70 degrees of air outside the rad.

With hot water radiation you should get about 170 BTU's per sq. ft. when the water temp. is 180 degrees.

The question I have is related  to  the latent heat of vaporization. If you have 215 degrees of water ( pressurized, of course) in a radiator, how many BTU's would be released per sq. ft. of radiation?

Would it be the same 240? Shouldn't be less due to the fact that you are not releasing latent heat? If so, how many BTU's per EDR?

Looking to clarify the whole EDR thing at that boiling point temperature regardless of pressure, if that makes any sense.


  • EDR

    Wow! That's a good question and I don't have an answer. 

    Theoretically, the radiator filled with steam at 215F will put out more heat than a radiator filled with 215F water,  What is the difference in BTU's?

    And if you look at the EDR table, the output is linear; there is no big jump at 215F where steam gives up it's latent heat.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • VA_Bear
    VA_Bear Member Posts: 50
    OK, Why?

    Are you trying to convert a steam system to hot water? I can't figure why you would want to want to take the risks of running a hot water system at 215 deg...
  • steamfitter
    steamfitter Member Posts: 156
    latent heat

    That's the thing that's haunting me. We know that it takes 180 btus to get a pound of water from 32 degrees F to 212 degrees F and it takes 970 btus for that same amount of water to become steam.

    If 1 edr is equal to 240 btus for steam does it mean when it's condensing and releasing all of its heat energy? Is there a different amount of btus for water @ 212 degrees F?

    Not looking to do anything with this in regards to a hw or steam system, just trying to clarify the science.
  • Eastman
    Eastman Member Posts: 927
    It's based on the tempreture delta

    between the rads surface and the rooms air.  215 water would be the same as 215 steam.
  • Weezbo
    Weezbo Member Posts: 6,232
    edited October 2013
    last week or so,...

    i was considering super saturated steam and nozzle steam injection etc and spent quite a bit of time reading . there is a chance though that i erased that after reading ..i think the title of the paper was on some search i was doing on smallest steam boilers which happens to be something that is used in like garmet industry for pressing materials ...

    i will see if i can find the one of three down loads i read . it has all the minor technicalities i am pretty sure it was not the cleaver brooks steam boiler manual.

    here is one ....


    Internal relaxation processes in wet steam flows

    through channels and nozzles are analysed basing on derived general equations describing non-equilibrium wet steam processes. Characteristic relaxation distances for single-deviation processes are determined and their application is discussed. As a synthetic intensity measure of complex multi-parameter processes a concept of entropy relaxation distance is introduced. Calculation methods of wet steam relaxation processes and thermodynamic loss determination are presented

    this might bring up his book Andrjez Koronski

    here is an aside that i read while looking for the boiler designes .


    and yet another .


    these are small heat exchangers .

    i havent found the mini books i read just yet ,

    however there is a guy who has a hot water heater he was using for his heat off a solar array for power and i started to consider the pros and cons of miniature in specialty steam products and boiler manufacturing and a variety of other things working within the parameters of what he has....

    Ok go here


    this is where i did the most reading ....

    and this i also read right rapid.


    these things give you a really clear understanding of the parameters and whys and wherefores of steam boiler manufacturing and conveyance over to a water system Steam would seem to be the guys best way to roll without large expenditures of electrical energy.

    as he relies upon PV for juice.
  • Jamie Hall
    Jamie Hall Member Posts: 22,972
    You will get

    the same 240 BTU per square foot with water at 215 as you will with condensing steam -- also at 215.  Trouble is, a pound of steam condensing releases 1,000 BTU.  A drop in water temperature of 1 degree releases 1 BTU per pound.  So... you will need an awful lot of water going through that radiator, in terms of pounds, to get the amount of heat out of it that you would get with 1 pound of steam.  if you wanted to hold the whole radiator at 214 with water -- to get almost the heat you would out of steam you could tolerate only a 2 degree drop in water temperature (215 in, 213 out, 214 average) or 500 pounds of water to do what 1 pound of steam would do.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • steamfitter
    steamfitter Member Posts: 156
    great explanation!

    Thank you for clarifying that for me. That explanation clearly brings to light how powerful the thermal energy of steam is.
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